As is known in the art, existing automotive radar systems detect targets which produce a radar return signal having a signal strength which exceeds a threshold signal strength in range/Doppler space. The radar then develops an estimate of X-Y position and velocity for each target. This approach typically requires algorithms in the form of state machines and tracking with thresholds and heuristics.
As is also known, the classic implementation of synthetic aperture radar (SAR) generates images of objects on the ground from the air. By using relative movement between a ground object and an airborne platform (e.g. an airplane or a satellite) on which the SAR is mounted, the antenna is made to seem much larger than it is because the moving platform allows the SAR to repeatedly take measurements of the object from different positions. In general, SAR systems coherently combine amplitude and phase information of radar return signals from a plurality of sequentially transmitted pulses using a relatively small antenna mounted on the moving platform. A processor then integrates these signals to make them seem as though they came from a large stationary antenna rather than a relatively small moving antenna. Thus, a SAR provides a way to use signals received at multiple antenna positions to improve an angular resolution characteristic of the radar.
Conventional SAR systems (e.g. those mounted on and operating from an aircraft or satellite) typically have relatively good range resolution and relatively poor angle resolution. Synthesizing a large aperture allows the system to achieve an angle accuracy similar to range resolution. This allows the SAR system to generate an image of the ground (or infrastructure) having the same resolution in X and Y coordinates. Also, the SAR is directed toward objects very far away from the radar compared to the motion of the platform. This allows SAR systems to utilize simplifying geometrical assumptions when processing measured data. Simple SAR assumes a linear host path, constant velocity, and targets at very large distances compared with the length of the synthetic aperture. Conventional SAR systems can use such simplifying assumptions to optimize the mathematical calculations which enable the use of a fast Fourier transform (FFT) to form a target image. Also, numerous SAR techniques are known for “stretching” or partly violating the assumptions while still retaining the advantages of using the FFT to form a SAR image.